"My Dearest Baby, You gave me the strength I didn’t know I had," she began her letter. "You taught me the true meaning of serenity and peace. I can't wait to meet you. I can't wait for you to join the players box next year. But most importantly, I am so happy to share being number one in the world with you.... once again today...from the world's oldest number one to the world's youngest number one. -Your Mommy"

And followers eagerly congratulated Williams on her tandem achievements, noting her baby will be in very capable hands.

"Once number one, always number one. Imagine how proud your baby will be once realizing what you represent for the rest of the world," one wrote, while another noted "God has truly blessed you. I believe you are the Greatest Athlete Ever regardless of gender."